From the prior art, a device for increasing functional safety by monitoring the current set in a two-wire current loop has become known from European Patent, EP 2274656 Al. For this, an evaluation unit is provided which monitors the current set by the current regulator in the two-wire current loop. In the event of a defect, the current controller (OPV) leaves its operating range, to compensate for a leakage current for example. This can be detected by the evaluation unit and a corresponding error signal can be initiated.
However, here the disadvantage is that an error in the control electronics itself cannot be identified, and it is only possible to check whether the transmitted signal was also set in the current loop.